The use of torque limiting clutches to couple drive and driven members is well known. In industries requiring such torque limiting clutches, it is well known that the same are designed or selected for specific applications. Each torque limiting clutch typically has a characteristic break-away torque. By employing a torque limiting clutch with a break-away torque which is lower than that at which damage can be done to the drive or driven members, the torque limiting clutch serves to protect the system in which it is employed.
Previously, it has been known to use spring bolts, spring pins and/or spring cups in torque limiting clutches as a force generating means. Such spring bolt assemblies are shown in U.S. Pat. No. 4,401,426, such spring pin assemblies are shown in U.S. Pat. No. 4,645,472, and the spring cup assemblies of a similar nature are shown in U.S. Pat. No. 4,661,083. It is now readily appreciated by those skilled in the art that such spring bolt assemblies, spring pin assemblies, and spring cup assemblies provide for ease of assembly of torque limiting clutches. They further significantly preclude tampering with the torque setting of the clutch, and provide substantially consistent characteristic break-away torque over the useful life of the clutch.
Despite the compact nature of the spring cups, spring pins, and spring bolts, torque limiting clutches are necessarily of substantial physical size, particularly length. This size results from the necessary inclusion of input and output coupling members, a pressure plate, spring or other force members, and the requisite number of friction elements. The physical size constraints placed on many systems otherwise requiring torque protection often preclude the implementation of torque limiting clutches therein.
It is well known in the art that the size of many torque limiting clutches is often dictated by the assembly techniques employed in their manufacturer, such assembly requiring access areas to nuts, bolts, and the like during the assembly process. When such nuts and bolts are interior to the torque limiting clutch, access openings and clearances must be provided within the clutch to accommodate the assembly process. These areas and openings necessarily aggravate the size considerations given in the design of such torque limiters.
It is further known that the size of a torque limiting clutch is greatly impacted by the nature of the input and output hubs employed for the coupling of drive and driven members thereto. In many known torque limiting clutches, the axial size of the clutch, measured axially from one extreme to the other, has been found to be excessive.
Prior torque limiting clutches have generally failed to provide adequate heat dissipation in a compact unit, and have generally been ineffective in shielding the interior of the clutch from the environment. Such shielding is required to prevent contamination of the friction surfaces, and thereby provides for more accurate torque characteristics.
Additionally, the known prior art has generally not provided for the use of wear indicators to advise the operator when the friction material has been spent.
There is a need in the art for a compact torque limiting clutch of minimal axial dimensions and in which its assembly is easily achieved without the need of access to the internal structure of the assembly. There is a further need for such a torque limiting clutch which achieves effective heat dissipation and protection from the environment while assuring coaxial alignment of the input and output members. There is also the need for such a torque limiting clutch that employs a torque pin as a wear indicator.